The briquetting machine produces the briquettes by successively supplying the materials or the raw materials between a pair of rotating rolls and applying a high-compressive force to the supplied materials (see Patent Documents 1 and 2, for example).
The quality control in the production process of the briquettes produced by the briquetting machine can be done by an operator regularly sampling a part of the produced briquettes and determining the state of the sampled briquette (i.e., briquette sample) as a numerical value in consideration of the physical properties such as the apparent density, the crush strength, and the like. It is noted that the apparent density can be calculated by volume and weight of a briquette.
Conventionally, as a method of measuring the volume of the briquette, the briquette taken as a sample is immersed in a liquid of paraffin or the like (without briquette solubility) in a container such as a measuring cylinder, and an increase in its liquid level is measured.